Junta chief Prayut Chan-O-Cha said the bombing was the "worst ever attack" on Thailand and that the hunt was on for the bomber filmed on closed-circuit television at the shrine, as well as a motorcycle taxi driver, who drove the man away.

While authorities did not say whether the suspects had any known motives, here are some of the culprits who could be responsible for the attack.

Red Shirts

For: The Red Shirts group has been fighting the military government since it came to power in a coup last year. Initially the government said it believed the bomber was from the north-east of the country, where the Red Shirts have their power base.

Against: Most Thai analysts say that it is just highly unlikely that they would do this. Not only would it be a huge step up in their campaign, which has been very low-level violence so far, but more importantly they would just lose the moral high ground. They would just lose their support, which is big in the population here, so it is unlikely they would do it.

Islamic insurgents from southern Thailand

For: They have been fighting the government for decades.

Against: It does not have their hallmarks. They have contained their attacks to the south and they have targeted generally property, not people.

They also have never attacked tourism sites at all, while the shrine was a huge tourism site for both foreigners and also Thais.

Islamic State

For: This was a Hindu shrine. Obviously it does not accord with their fundamental ideology.

Against: People are asking why Thailand, and why now? Thailand really has very little support at all for the efforts against Islamic State in Syria and Iraq — in fact, hardly none — so why? And then if you look at Islamic State's attacks, analysts are also saying that they probably would have gone after the beach resorts like Phuket or Koh Samui and really target foreigners there on the beach as they did in Tunisia.